System capacity and communication quality are two crucial indexes, which used for assessing the performance of a mobile communication system. Generally, system capacity shows the number of users that can be served by a system simultaneously. Bigger system capacity brings higher profits for operators. Communication quality of the system indicates the quality of services provided by the system for users, and better communication quality means higher client satisfaction and higher profits for operators.
However, system capacity and communication quality may conflict because of the soft capacity, a unique feature of the CDMA system. That is, the system capacity usually expands at the price of communication quality while the communication quality in the system, similarly, improves at the price of system capacity. Therefore simultaneous optimization of both the system capacity and the communication quality in the CDMA system is a subject highlighted at present.
In a conventional CDMA system, a Base Station Controller (BSC) stores power control parameters and handoff parameters of all base stations (BSs) covered by the BSC. The parameters are configured in an initiation process of the CDMA system and usually remain unchanged.
The power control parameters include: a maximum transmit power threshold of a forward channel of a BS, a minimum transmit power threshold of the forward channel of the BS, etc. The maximum transmit power threshold defines the maximum transmit power available to the BS, and the minimum transmit power threshold defines the minimum transmit power available to the BS.
The handoff parameters may include a maximum active set branch threshold, a pilot add threshold (Tadd), a pilot drop threshold (Tdrop), a pilot compare threshold (Tcomp), a dynamic soft handoff slope, a dynamic soft handoff add intercept, a dynamic soft handoff drop intercept and a pilot drop time threshold (Ttdrop), etc.
Through at least one of the power control parameters and the handoff parameters, the BSC controls mobile stations to perform soft handover. For example, on the one hand, the higher the maximum transmit power threshold of the forward channel of the BS is, which is assigned by the CDMA system to the BS, the greater the power available to the BS will be, and the better the communication quality will be; on the other hand, the greater transmit power adopted by the BS may bring interference to other users in the same cell or in adjacent cells, which further leads to capacity drop in the CDMA system.
For another example, a greater maximum active set branch threshold, which is configured by the system, brings larger number of BSs which are allowed to concurrently communicate with a mobile station, therefore mobile stations obtain more soft handover gains and better communication quality. However, the fact that the mobile stations occupy more radio channels leads to system capacity drop.
The applicant finds out that the communication quality between the BSs and the mobile stations can be adjusted by modifying the power control parameters or the handoff parameters.
Conventionally, the power control parameters and the handoff parameters are fixed values stored in databases of BSCs. All mobile stations covered by a same BS share the same parameters which remain unchanged during calls, without regard to the strength of the CDMA signals. However, CDMA signals may be strong in parts of the area and weak in other parts of the area, because of factors such as the geographical environment. For this reason, the communication quality is not satisfied and the call-drop rate are often high in the parts where CDMA signals are weak.